The present invention relates to a high-density magnetic recording method and to a magnetic recording apparatus for carrying out the method.
Conventionally, there has been known an apparatus which records a signal on a magnetic recording medium through a magnetic head and reproduces the signal from the magnetic recording medium through the magnetic head. An example of such an apparatus is a magnetic disk apparatus. Also, a magneto-optical recording apparatus has been known. In the magneto-optical recording apparatus, a signal is recorded on a recording medium by a magnetic head while a laser beam is radiated onto the recording medium, and a recorded signal is reproduced by Kerr rotation of the laser beam. An example of such a magneto-optical recording apparatus is an optical disk drive in which a laser is radiated onto a recording medium to change the state thereof in order to record a signal, and the change in the state is detected in order to reproduce the signal. Recording methods and apparatuses of these types have realized a recording density of 1 GB/cm2 and are expected to realize a recording density of 10 GB/cm2 in the future.
However, when a huge amount of data must be processed, the above-described recording density of 1 to 10 GB/cm2 is insufficient. Therefore, the conventional methods and apparatuses are not satisfactory.
Incidentally, existence of spin vortices has been observed for Co fine particle [A. Tonomura et al., Phys. Rev. Lett., Vol. 44 No. 21 (1980), p. 1430].
Further, a study on a magnetization process of thin film of permalloy fine particles revealed a phenomenon in which spin vortices are generated in the course of formation of magnetic domains [D. R. Fredkin et al., IEEE Trans. MAG, Vol. 26 No. 5 (1990), p. 1518; K. Ruage et al., J. Appl. Phys., Vol. 79 No. 8 (1996), p. 5075].
Moreover, in a computer simulation of magnetization process of a circular sample such as of Ba-ferrite having a large uniaxial magnetic anisotropy, calculation has been performed on the premise of a spin vortex structure [Y. Ishii et al., J. Appl. Phys., Vol. 81 No. 4 (1997) p. 1847).
Although mere observation and studies on magnetic structures have been performed, an idea of utilizing spin vortices for magnetic recording has not been proposed.
In order to utilize spin vortices for magnetic recording, the present inventors theoretically elucidated a mechanism and conditions for formation of spin vortices within a magnetic thin film, and discovered the relationship between the formation of spin vortices and the magnetism of the thin film. Further, on the basis of this finding, the present inventors discovered conditions for writing, reading, or overwriting a signal for the case where each spin vortex is used as a recording unit, and found that despite a recording unit having a very small size of about 10 nm, spin vortices are magnetically and thermally stable and therefore can be practically used for magnetic recording.
The present invention proposes a novel magnetic recording method and apparatus in which each spin vortex is used as a recording unit, as well as properties of a magnetic head and properties of a magnetic thin film serving as a magnetic recording medium, which properties are peculiar to spin vortex recording.
In view of the foregoing, an object of the present invention is to provide a magnetic recording method and apparatus which utilize a spin vortex as a recording unit and which enable high density recording.
To achieve the object, the present invention provides the following methods and apparatuses.
(1) A magnetic recording method in which a signal magnetic field is applied to a fine region of a magnetic thin film in order to form a spin vortex composed of a magnetization region surrounding circularly the perpendicular magnetization axis at the center, to thereby record a signal, and a direction and magnitude of magnetization of the spin vortex is detected in order to reproduce the recorded signal.
(2) A magnetic recording method described in (1) above, wherein the direction of magnetization of a spin vortex corresponding to a recorded signal is reversed in order to overwrite the recorded signal.
(3) A magnetic recording method described in (2) above, wherein recording or overwriting of a signal is performed while the magnetic thin film is heated.
(4) A magnetic recording method described in (2) above, wherein any one of recording, overwriting and reproduction of a signal or a combination thereof is performed by use of a columnar magnetic needle.
(5) A magnetic recording method described in (1) above, wherein a recorded signal is erased through thermal demagnetization of the magnetic thin film.
(6) A magnetic recording apparatus comprising:
a magnetic thin film on which, upon application of a signal magnetic field to a fine region thereof, a spin vortex composed of a magnetized region surrounding circularly the perpendicular magnetization axis at the center is formed;
signal recording means for recording a signal onto the magnetic thin film; and
signal reproduction means for detecting a direction and magnitude of magnetization of the spin vortex in order to reproduce the recorded signal.
(7) A magnetic recording apparatus described in (6) above, wherein the magnetic thin film is formed of a super-thin film having a thickness substantially equal to or less than the thickness of a domain wall.
(8) A magnetic recording apparatus described in (6) above, wherein the magnetic thin film is formed of a magnetic thin film having low in-plane magnetic anisotropy.
(9) A magnetic recording apparatus described in (6) above, wherein the magnetic thin film has an easy axis perpendicular to the surface of the magnetic thin film.
(10) A magnetic recording apparatus described in (6) above, wherein the magnetic thin film is formed of an array of circular thin films.
(11) A magnetic recording apparatus described in (6) above, wherein the magnetic thin film is formed on a grid of soft magnetic thin wires.
(12) A magnetic recording apparatus described in (6) above, wherein the magnetic thin film is a thin film formed on an array of disks each made of a material having a high magnetic flux density and having a diameter smaller than that of a spin vortex.
(13) A magnetic recording apparatus described in (6) above, wherein the magnetic thin film is a thin film formed on an array of disks each made of a magnet or an antiferromagnetic material and having a diameter smaller than that of a spin vortex, so that the magnetic thin film has local perpendicular magnetic anisotropy at a position corresponding to each disk.
(14) A magnetic recording apparatus described in (6) further comprising means for overwriting a recorded signal by reversing direction of magnetization of a spin vortex corresponding to the recorded signal.
(15) A magnetic recording apparatus described in (6) further comprising means for heating the magnetic thin film when a signal is recorded or overwritten on the magnetic thin film.
(16) A magnetic recording apparatus described in (6) further comprising means for erasing a recorded signal through thermal demagnetization of the magnetic thin film.
(17) A magnetic recording apparatus described in (6) further comprising a columnar magnetic needle which is used for any one of recording, overwriting, and reproducing of a signal or a combination thereof.
The magnetic recording method and apparatus according to the present invention enable recording at a high density of 1 TB/cm2, so that a compact storage device having a large capacity of a terabit order can be provided.
Although the magnetic recording method and apparatus according to the present invention are based on magnetic recording, use of spin vortices for magnetic recording enables construction of theoretically new recording units to thereby enable realization of a recording density 1000 times that achieved by conventional methods.